Aircraft blind landing system



Aug. 29, 1939. H. CHIREIX AIRCRAFT BLIND LANDING SYSTEM 2 Sheets-Sheet 2 Filed July 30, 1936 M Etxifii QREEEQ o 5563 59.5% m

INVENTOR HENRI C IREIX ATTORNEY Patented Aug. 29, 1939 2 17 852 AIRCRAFT BLIND LANDING SYSTEM Henri Chireix, Paris, France, assignor to mpagnie Generale dc Telegraphic sans Fil, a corporation of France Application July 30, 1936, Serial No. 93,333 In France August 9, 1935 9 Claims. (01. 250-11) This invention relates to antenna systems, metallic reflection will thus be produced, and the particularly for blind landing beacons for airfield picked up in the vertical plane will be incraft. The system contemplates the use of ultradependent of the height, at least as long as a short waves and arrangements for rendering small angle of incidence 'r is maintained, which these waves effective in much the same manner is usually the case.

as long waves would be but having certain ad- By taking certain necessary precautions I have vantages over the propagation of long waves. found that ultra-short waves can be reflected in The invention itself will be described in the much the same manner as long waves. One following specification, reference being made to essential consideration is that the height a above the accompanying drawings in which the counterpoise should be small in contrast with m Fig. 1 shows diagrammatically and in elevation the length thereof. The ratio of these two quantian antenna system suitable for carrying out my ties expresses the minimum slope corresponding invention; to metallic reflection. For angles of incidence Fig. 2 shows a diagram of the geographic dismore pronounced than this slope, the field at position of the direction beams with respect to distance x will be of this form 5 spaced antennae of the type shown in Fig. 1;

Figs. 3 and 4 are cross-sectional diagrams on K- g geritri cal planes erected upon the ground axis the term I Figs. 5 and 6 show respectlvely and diagram- 20 X matically elevation sketches of certain antenna systems and their directional beams; and heldmg good for the pl'opa'gatlon of sphencal Fig. 7 is a preferred circuit diagram for re- Wavesceivmg apparatus f l in connection with the For purposes of illustration the height 0: W111 be 5 invention assumed to be '50 cm. and the length of the F'jg 1 shhws an antenna comprising two Verfi counterpoise 100 meters, whence aminimum slope cal elements 2! and 22 surmounted by terminal of capacitances consisting, for example, of discs C L which are positioned preferably in a horizontal 200 plane at a height a above t ground level The The network of wires is preferably raised above 30 two vertical elements 2! and 22 are united by a ground and buried a certain distance towards the horizontal element 23 which is excited and enerd gized in its middle by means of a toroidal wind- The 1 t field on t other hand, is t ing s Winding m y e connected by cally polarized, and it may be assumed that the ea s of transmission line 25 to y Suitable horizontal disposition of the conductor 23 and of 5 source 26 of mod la e u r h f q n y siethe discs C win bring about this result. na s y. f the di si ns f th system Fig. 2 illustrates a case where two identical are so selected that the assembly is tuned to the Systems are l d, ch system being an emhalf-wave, that is to say, so that a standing wave h t of t t ture shown in Fig. l. The

Occurs having D in e neighborhood of the systems are spaced apart from center to center 40 toroidal winding 24, then the directional charby i t D nd their axes are oriented along acteristics of the radiation in a horizontal plane the line joining t Thi di t 1) forms a Will be those Of a frame antenna- In base line perpendicular to the two lines of zero ot Words, all a given distance the field will signal field intensity. The median line 33 is also vary substantially as the sine of where the Shown 45 angle 1 is formed by a line perpenicular to the Now, it will be noted that for an observer 1ohorizontal conductor 23 and a line representing Gated at M in Channel thus formed and the direction of radiation toward an observer. at a distance sumciently great compared with Along a Vertical the diagram Win essen D, the sum total of the fields coming in from the tially depend upon the quality of the soil or t frame aerials is of t i form; 50

ground at the place where reflection of waves D D takes place. It is sometimes found to be practi- I --y --+y K 2 2 K.D cable to employ a very close network of metallic x X jl= X2 (1) wires as a counterpoise ahead of the transmitting system and towards the observer. A so-called Where K is a constant. 55

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The total of the fields is thus constant throughout the whole channel of width D defined or marked by the extinction lines of the two frames.

For an observer located at M" outside the channel, the same sum would have this form:

X X X where are is the distance corresponding to value E0. Now, if the difference between the fields coming in from the two antennae be considered rather than their sum, it will be noted in contrast'that this difference'is constant and of a given sign for an observer located to the rightor left-hand side of the channel and that it varies within the channel from a positive value to a negative value, to become zero on the line 33. What is here meant by positive or negative is only that the signal coming in from the antenna 3| predominates over that received from antenna 32. 1

From the foregoing description it will be noticed that successive signals may be sent out on the same wave length, but with dissimilar modulation frequencies with a View to differentiating or distinguishing these two antennae. In a first indicator device I obtain an additive measure of the rectified currents resulting from double detection of the high frequency and the modulation frequency. In a second indicator device the difference between the rectified currents derived from the respective radiations from the two transmitting antennae is measured. The first indicator device, for a constant sensitiveness of the receiver, will result in a constant amplitude deflection throughout the channel width, and such indication will be inversely proportional to the square of the distance, whereas the second indicator will insure very effective guiding along the median line of the channel or course, because the differential current passes through zero in midchannel. The indicator pointer will, therefore, swing to the left or right of a normal mid-position according to whether the craft is on the left-or the right-hand side of the course. The sensitiveness of the receiver is preferably adjusted by means of an automatic volume control device presently to be described. The first mentioned indicating device may then be rendered capable of use for indicating altitude.

Referring now to Fig.5, the antenna 5! consists essentially of a horizontal doublet with ground of low conducting powers in the neighborhood, this being a practical case for ultra-short waves and for an angle of incidence so small that sine 'r 0.1.

It will then be noted that for an observer placed in the vertical plane containing the doublet and seeing the latter under a small angle of incidence, the electric field reaching him will be polarized almost perpendicularly, and that, moreover, the refiection from the ground occurring in phase oppo sition, the incident ray E1 and the reflected ray E1: become added iii-phase (save for existing differences in path). This follows from an examwhere it represents the height of the observation point.

For vertical planes being slightly inclined in reference to that containing the doublet, it can be readily seenthat the horizontal components of the introduced fields do not play an important part, at least so far as antennae that are low in a reference to the wave length are concerned, be-

cause of the fact that they are suppressed and destroyed owing to reflection from the ground. What follows therefrom is that when the vertical plane containing the doublet and an observer stands at a small angle in reference to the axis of the incoming beam, the radiation is vertically polarized and is of a form indicated by the equation given in the preceding paragraph.

Summarizing, this antenna system provides the same field diagram or characteristic as a vertical antenna placed above a poorly-conducting ground. However, it is believed-and this is an important feature of the present inventionthat the influence of the ground is far less noticeable in the caseof this antenna than of the so-called doublet generally employed in systems used for blind landing.

As a matter of fact, the efiect of the earth manifests itself only in the geometric composition'of two small vectors sensibly of the same amplitude and practically in phase. If the angle of the composition or the amplitude varies a few of'the doublet type will now be considered. These 1 antennae are spaced apart by a distance D forming a base. The two antennae as well as the base Dare contained in .one'and the same vertical plane. For an observer placed at a distance inside the same plane or a little apart from it, the

sum total of the fields coming in from these two antennae at a fairly great distance will be of. this form:

where K is a constant, while the difference of the fields that are received will be of this shape:'

In the light of the foregoing discussion it will I be seen that if signals are sent out sequentially on the same wave length, though with different modulation frequencies, from antennae 35 and 36 in order to differentiate these signals, the sum of the incoming currents after double detection will be proportional to the square of the distance,

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whereas the difference will be proportional still to the height, but to the third power of the distance.

The foregoing considerations regarding the properties of such antennae will make it an easy matter to understand the operation of the antenna systems here disclosed. Antenna systems of this kind insure landing in the absence of visibility of airplanes, while furnishing the craft at the same time with uninterrupted indications so as to keep the craft on its course without lateral deviation, keep it at the proper altitude above ground, and inform the pilot of the distance to the landing field. For this purpose four distinct antenna systems 3|, 32, 35, 36 are employed as shown in Fig. 6. Antennae 3| and 32 are spaced apart from each other by the length of the base line D, measured at right angles to the landing line, and antennae 35 and 36 are separated by the base D measured along the landing line. The antennae 3i and 32 are preferably provided with counterpoise members M, 42 consisting of metallic wires, of sufficient size and suitably disposed ahead of the antennae themselves so that the reflection of the waves may be produced thereon. The reflection of the waves of antennae 35 and 36 occurs on the ground itself.

By the agency of a distributor device, antennae 3|, 35, 32 and 36 are sequentially fed with energy in any desired order, say, in the order just mentioned. A dissimilar modulation frequency is used for each of these signals so as to identify and distinguish the same in reference to one another. These modulation frequencies are herein denoted, respectively, f1, f5, f2 and f6.

It will be noted from what follows that if the sensitiveness or responsiveness of the receiver outfit installed on board the aircraft is regulated by an automatic volume control device with a view to stabilizing the sum total or the mean value of the signals from antennae 35 and 36 the following results will be obtained:

(1) One indicator instrument mounted and connected to be acted upon by the sum total of signals coming in from aerials 3! and 32 will register indications inversely proportional to the height, as follows from this formula:

(2) A second indicator device mounted and connected so as to be acted upon by the difference of the outputs or radiations from antennae SI and 32 will insure lateral guiding (zerotype apparatus), as flows from the following formula:

It will be clear that these results will hold good only as long as the receiver apparatus operates properly and the airplane flies within the course or channel of width D, that is tosay, as long as y is less than Fig. 7 shows by way of example a practicable embodiment of. a suitable audio frequency part of the receiver equipment. I denotes a power tube working upon a transformer 2 having a secondary winding with an intermediate tap so as to be able to tap, for instance, one-tenth the full potential. The rectified currents of the antennae 3! and 32, Fig. 6, modulated with frequencies f1 and f2 set up, by virtue of resonance, potentials across the terminals of the tuned circuits I and II, the energy being fed across the coupling capacitors 3 from the intermediate tap of the secondary winding on the transformer. 2.

Circuits I and II as well as circuits III and IV consist of capacitors Q and windings of transformers 5 preferably having a voltage step-up ratio between primary and secondary. These transformers are preferably of the iron-dust magnetic-core type in order to insure satisfactory selection. 6 denotes dry detectors, say, detectcrs of the copper oxide or selenium oxide type. I and 8, respectively, stand for resistances of high value, say, of an order of 100,000 ohms, and for large capacities, in order that there may result an adequate time constant. 9 and ii! are two direct current moving coil type milliammeters. 9 is a differential device, that is to say, comprising a coil with center tap, and I designates preferably an instrument with a so-called logarithmic scale in which the graduations are crowded together at one end of the scale. It will be noted that device 9 responds to the difference of intensities coming in from circuits I and II. Device 9 thus serves as a guiding apparatus, the needle occupying the middle of the scale when there is no difference between the opposing forces of the two circuits I and II. Device ID, on the contrary, is traversed by the total of the detected currents. Hence, it will register inverse height values, provided that the responsiveness of the receiver is regulated by the aforementioned automatic volume control device.

For obtaining distance measurements, the rectified currents originating from antennae 35 and 36 set up potentials having modulation frequencies f3 and f4, across the terminals of the tuned circuits III and IV which are coupled to the transformer 2 by way of capacitor 3'. The elements 4', 5, 6', l" and 8 correspond with the aforementioned elements 4 to 8 inclusive.

The antennae 35 and 36 thus create across the terminals of resistances I potentials which are additive. These potentials may be used for the regulation of the receiver, as will be pointed out presently. The high voltage direct current source which feeds the receiver and whose negative pole is grounded, works upon a protection resistance I2 and a neon tube l3 serving to regulate the voltage across the terminals of the potentiometer l4. Tapped on the latter is a regulable countervoltage. The equipment further includes a rectifier l5 and the shunt-connected combination of the condenser l6 and the high ohm resistance 51. It will be readily seen that as soon as the sum of rectified voltages across the terminals of resistances l exceeds the voltage furnished from the potentiometer l4, a current is set ufp in the rectifier l5, which current creates in turn a negative voltage in IS. This negative potential is impressed directly upon the grids of amplifying tubes (not shown) of the receiver and occasions a so much more marked regulation of the latter the higher the countervoltage taken from (tapped on) the potentiometer I4. It will be noticed, finally, that the device I9, being of the moving coil type preferably with a logarithmic scale, is traversed by the difference of the detected currents of circuits III and IV. Its readings will thus be proportional to the distance, as has h-ereinabove been pointed out. The switch 20 finally serves to change the responsiveness for devices 9 and I0 furnishing guiding and altitude data.

When the said throw-over switch 20 is in position a, the voltages set upacross the terminals of the transformer 2, by virtue of regulation, will be 10 times higher than when placed on terminal b, thus increasing the sensitiveness of the receiver tenfold. The position a is used during the first stage of the landing operation, the signals being weak due to distance;

The currents flowing through the instruments 9 and I!) being, respectively, proportional to D/n and Y/h grow at a rapid rate in a measure as the airplane loses altitude and approaches the field up to the instant when the device attains its maximum deflection. The throwing of the switch 20 from position a .to position b will then diminish the sensitiveness, say, at the ratio of 10 to 1, and this results in readings or indications on a new scale on which the graduations start from a current value ten times smaller.

.The meter reading finally reaches maximum at the very instantof landing. If, for instance, the mean altitude of the receiving antenna is 5 meters above the level of the wheel base, then the throw may be accomplished at a height of 50 meters so that, for a measuring instrument covering a range of 26 decibels, there would be a first scale from 1000 meters to 50 meters and a second one from 100 meters to- 5 meters corresponding, as a matter of fact, torzero altitude of the wheels above ground. The extent to which the sensitivity and the precision inherent in this arrangement grows will be noted during the final phase of the landing operation. This is due to the selection of the antenna provided for regulating the receiver. The indications given are then the inverse of the distances and the altitudes, and the consequence is that the currents flowing through the devices will reach a crest value at the exact time of landing. It will also be noted that, although the pilot is able to follow any landing curve at all, the sensitiveness of the receiver will not vary' if he follows a parabolic descending or glide curve, in line with what is customarily done in present day practice, the operation and regulation effectively predicated upon antennae resulting in a field of the shape so that regulation of the receiver is facilitated However, it is possible to obthe difference in the incoming fields, indeed, is of this form:

sumv of the current flowing through I0 provided the guiding is accurate. This circumstance may be of a certain" practical interest during the initial stage of the landing operation when the pilot is not necessarily or strictly inside the zone of his course.

Inasmuch as the operation of the wholescheme is predicate-d upon the proper and precise operation of the automatic volume control means, it will be imperative to insure proper operation of the latter. With this end in view, a marginal relay 3'! is preferably included in the output circuit of the receiver; When the automatic volume control device goes into action the relay actuates an annunciator or lamp 38 mounted on the instrument board. Suitable connections for the relay'31 are shown in Fig. 7 where itappears in series with the meter [9.

It must be understood that the particular embodiment and form: of construction which has been disclosed hereinbefore with a number of detailed features with a view to facilitating the proper understanding of this invention, is capable of a great number of'modifications, both as regards the sending aerials as well as'the dispositions of the receiver equipment. Antennae 35 and 3 6, for instance, could be vertical doublets. Instead of producing with a single transmitter four signals or transmissions differentiated by means of their respective modulation frequencies, it. would also be feasible to work with four simul taneous transmissions upon slightly different wave lengths and modulated by dissimilar fre- But in this case the range of recepquencies. tion of the receiver would have to be enlarged.

It would even be possible to produce four simultaneous transmissions upon slightly dissimilar wave lengths'without modulating these waves. It will be suflicient for them to be adequately stable from the viewpoint of their frequency, and to be received in a heterodyne type of receiver apparatus which likewise must be highly stable. The circuits I, II, III, and IV provided in Fig. '7 would then be tuned directly to the intermediate or transfer frequencies. It seems, however, that these solutions are more complicated and less practical than those hereinbefore described.

I claim: 7

1. A radio beam transmitter for ultra-short waves comprising an antenna system having two upright conductors joined at the base by a horizontal conductor and having means including disc shaped capacitive members topping each upright conductor for producing a vertical polarization of energy radiated from said antenna system, means including a toroidal winding surrounding said horizontal'conductor at the midpoint thereof for energizing said antenna system, means for characterizing the energization as standing waves in the antenna system, and means for extending thefield of influence of said transmitter in at least one direction, said means comprising a close network of conductors disposed at or near a the ground level at a suitable region for reflecting the radio beam.

2. Blindlanding'system for aircraft comprising a transmitter feeding radio frequency to two antennae disposed on a line perpendicular to the landing direction, each of said antennae having two vertical conductors located in the plane passing through said perpendicular line, said conductors being connected at their base by a horizontal conductq and having concentric capacities topping said vertical conductors, a feeding line between the transmitter and a separate toroidal winding disposed respectively surrounding each of said horizontal conductors, a net of conductors disposed essentially on the ground before each conductor in the landing direction, and means for modulating the radio frequency fed to the antenna by different characteristic frequencies.

3. Blind landing system for aircraft comprising a transmitter feeding high frequency to four antennae, two of which are disposed in a line perpendicular to the landing direction, each of said two antennae having two vertical conductors located in the plane passing through said perpendicular line, said conductors being connected at the base by a horizontal conductor and having concentric capacities topping said vertical conductors, a feeding line between the transmitter and a separate toroidal winding disposed respectively surrounding each of said horizontal conductors, a net of conductors disposed essentially on the ground before each conductor in the landing direction, two other of said four antennae each formed by a horizontal doublet insulated from the ground and extending in the landing direction, said last mentioned antennae being located in the symmetrical axis between two first antennas and symmetrically in regard to the point of crossing of said axis with said perpendicular line, and means for modulating the radio frequency fed to said four antennae by different characteristic frequencies.

4. Aircraft receiver for signals transmitted by a system according to claim '7, comprising means for selecting different characteristic frequencies, means comprising detectors for obtaining direct currents proportional to the carrier amplitudes of said different frequencies, means responding to the sum of the currents corresponding to the second pair of antennae for controlling the steadiness of amplitude ahead of the detectors, an indicating device responding to the difference of currents corresponding to the second pair of antennae, and two further indicators responding respectively to the sum and to the difference of the currents corresponding to the two first antennae.

A system according to claim 3 in combination with a receiver comprising a detecting circuit means and having warning means comprising a relay connected in the detected current circuit so as to be traversed by the difference of the currents derived from the second pair of antennae.

6. A system according to claim 3 in combination with a receiver having means for controlling the amplitude of the currents whose modulations are derived from the second pair of transmitting antennae.

7. A blind landing system for aircraft comprising two separate transmitting antennae, each of said antennae having two separate vertical conductors and a horizontal conductor interconnecting the bases thereof, all four vertical conductors and the two horizontal conductors being disposed in a vertical plane substantially perpendicular to the intended direction of landing, means including a concentric capacitive plate mounted on top of each vertical conductor and serving to compensate for the capacitance between ground and the lower portions of said antennae, including the horizontal conductors, a separate toroidal inductive element surrounding the mid-portion of each horizontal conductor, a high frequency energy source and a transmission line connected to said toroidal elements, means for modulating the high frequency energy by different characteristic frequencies for each of the two said antennae, and means including a network of conductors disposed along the ground in front of said antennae for increasing the intensity of ground reflections of the radiant energy from said antennae.

8. A blind landing system for aircraft comprising first and second pairs of transmitting antennae, each antenna of the first pair being disposed transverse to the line of intended landing, and each antenna of the second pair being disposed along the intended direction of landing, each of said antennae of the first pair having two vertical conductors and a horizontal conductor interconnecting their bases, a concentric capacitive plate topping each vertical conductor, a radiant energy source and a feed line, a separate toroidal inductive element surrounding the mid-portion of each horizontal conductor and connected to said feed line for energization by said source, and means for modulating the energy differently as radiated by each antenna.

9. A blind landing system for aircraft comprising a transmitter as set forth in claim 12 and a receiver having detector means for obtaining direct currents proportional to the carrier amplitudes of the signals radiated by the different transmitting antennae, means responsive to the integrated currents derived from the second pair of transmitting antennae for controlling the volume of input energy applied to said detector means, an indicating device responsive to differentiation between the currents derived from the second pair of transmitting antennae, and two additional indicators connected to said detector means, one being responsive to the sum and the other to the difference of the currents derived from the first pair of transmitting antennae.

HENRI CHIREIX. 

